This invention generally concerns a coil form for air-cooled electric windings of a transformer and more particularly to a coil form with carrying means, disposed parallel to the longitudinal axis of the form, serving on one hand as a holder for an iron core and on the other hand as a carrier for at least one inner and one outer winding, with supporter means delimiting the carrying means at their faces.
One of the most current coil forms of the type concerned here consists of a square cylinder, which, at each of its faces, passes over into a collar-like flange, which, in respect to the compact shell, is perpendicularly directed to the outside. The cylinder covers the iron core, serving at the same time as a carrier for the inner winding. The outer winding is placed on bars, which are disposed between the flanges parallel to the longitudinal axis of the form, the ends of the bars fitting into radial rim slots at the corners of the flanges.
This known coil form has the considerable disadvantage that for coils of different size, production of coil forms of different size is necessary according to the requirements concerning the power and other electromagnetic properties. Even if the coils within a certain range of dimensions differ from each other only in one dimension, and thus in their length, width or height only, each of these coils requires a special coil form. These coil forms can only be produced by a pressing or die-casting process, so that for each size of coil form a special mold must be produced, and this requires a considerable expenditure. With regard to the need for the availability of all deliverable coil sizes within a certain period, independently of the real consumption of the different sizes, it is therefore necessary for the producers as well as for the consumers to keep in stock the complete large collection of coil forms. Such an extensive stock-keeping causes high costs and is, especially in small enterprises, often not realizable in the required volume because of lack of the necessary store-room.
It is a further disadvantage that the cylinder carrying the inner winding has a compact shell, because this prevents a sufficient air-circulation, which is indispensible for carrying off the heat produced during operation of the coil. In order to avoid this disadvantage the iron cores are made from a material of better quality, but this entails a considerable rise of production costs, especially in the case of transformers with large dimensions. Besides that, large quantities of material are required for the construction of these coil forms with compact shells, and costs will be increased if high quality and expensive material, as for instance glass fiber reinforced plastics, must be used because of the high temperature stability required.
It is the object of the present invention to create a coil form, which is adaptable to different sizes, permits a convenient air circulation between the windings, and the production of which is simple and requires small quantities of material.
According to the present invention this object is achieved by creating a coil form consisting as to all directions of plug elements, which are engageable with each other in a detachable way. A preferred model of this coil form has holders at its faces, which are designed as plug-in frames, in the clearances of which there can be inserted sets of carrying elements with variable length but with equal length within a set. The carrying elements take the form of profiled bars or distance pieces, and each plug-in frame is provided with at least three, by preference four, sides, each with a variable length. The ends of two adjacent sides pass respectively over into a flange directed to the outside, these figures being provided with a U-shaped channel for receiving the distance pieces at the sides of the plug-in frame pairs, which face each other.
The coil form, according to this invention, is superior to the conventional coil forms of this type by being designed on the basis of the mechanical assembly technique, thus permitting assembly by the simple fitting together of individual elements. It is possible to produce a large number of coil forms of different sizes by combining the framework-parts, which are necessary for obtaining two plug-in frames, and which have one and the same size, with sets of different length of side connection pieces and carrying elements.
A further advantage of the invented coil form is that its component parts can be produced in a simple and relatively cheap way by extrusion, stamping or pressing. Expensive production of molds is not necessary.
Additionally, the space saving storage and package of the component parts of the coil form represents another advantage for their stock-keeping and forwarding.